The invention relates to a fingertip sensor with a biometric sensor element for detecting fingerprints as disclosed in Published European Patent Application EP 0 805 247 A1.
To identify an ambulatory equipment user, for instance, personal identification numbers can be used. It is also known to detect characteristics specific to a given person for security purposes, such as fingerprints (minutiae) using biometric sensor elements and to enable or refuse access to equipment or a room and so forth, depending on the outcome of this detection. Detecting biometric characteristics of a person along these lines can be used either alone or in conjunction with identification numbers and provides a further, significant increase in security against unauthorized use.
Known biometric sensor elements include those with a piezoelectric layer, which ascertains local differences in capacitance under the control of an electrode array, and these differences can be used to recognize the minutiae. It is also known to call up the fingerprint directly with a capacitor array, which simply utilizes the height difference of the minutiae relative to the counterelectrode array.
However, especially for the sake of energy economy, a fingertip sensor of this type should be electrically activated and called up only during the fingertip contact. To that end, it is known to provide an additional proximity switch, which is coupled with the biometric sensor. This entails relatively great effort, however.
It is accordingly an object of the invention to provide a fingertip sensor with an integrated key switch that overcomes the above-mentioned disadvantages of the prior art devices of this general type, whose activation or deactivation can be accomplished in an especially simple, economical way when the sensor element is pressed and released.
With the foregoing and other objects in view there is provided, in accordance with the invention, a fingertip sensor, including: a biometric sensor element for detecting fingerprints; a sensor housing having a bottom part and a top part displaceable relative to the bottom part, the biometric sensor element retained on the top part; a spring operatively connected to at least one of the biometric sensor element and the top part, the spring generating a prestressing force for moving the biometric sensor element and the top part away from the bottom part; and a switch contact disposed on the bottom part for activating and deactivating the biometric sensor element, if the biometric sensor element is depressed the switch contact is closed, thereby effecting the activation of the biometric sensor element, and when the biometric sensor element is not depressed the switch contact is opened and the biometric sensor element is deactivated.
In the fingertip sensor of the invention, the sensor housing includes a bottom part and a top part that is displaceable relative to the bottom part, and the sensor element is retained on the top part. The sensor element and/or the top part is operatively connected to a spring, which generates a prestressing force that moves the sensor element and the top part away from the bottom part. A switch contact for activating or deactivating the fingertip sensor is also provided on the bottom part. When the sensor element is depressed it is closed, thereby effecting its activation, and when the sensor element is not depressed it is opened, so that the sensor element is deactivated.
The fingertip sensor of the invention makes activation or deactivation in a very simple, economical way. It is especially advantageous that the user can find the middle of the sensor field in tactile fashion, and the requisite finger pressure is at a minimum in that region. This assures reliable detection of the minutiae. The user also receives a mechanical (or under some conditions acoustical) xe2x80x9cacknowledgmentxe2x80x9d of a successful contact, when the sensor element strikes the switch contact. The rebound time is used to assure that the finger will touch the sensor for a long enough time. Another advantage is that the fingertip sensor of the invention can be integrated into the number pad of conventional telephones, and especially portable phones.
In an advantageous embodiment of the invention, the spring includes a leaf spring, which is secured to the bottom part and has a middle region that is convexly curved toward the sensor element and rests on the back side of the sensor element. Such leaf springs are economical and make a low-height configuration possible. At the same time, such a leaf spring can be used as a contacting element for closing the switch contact, so that no additional electronics are needed for that purpose.
Expediently, the top part has a chamfer extending all the way around and points toward a sensor field. As a result, the middle of the sensor field is easy to find by tactile methods, which makes it easy to find the precise finger position needed.
Advantageously, the top part in its peripheral region is guided mechanically inside guide recesses in the bottom part. This makes a very simple embodiment possible, without separate guide elements having to be glued or welded into place.
The housing may be manufactured of simple plastic injection-molded parts, for instance of ABS. The coloring of the top can be done in the course of constructing the apparatus.
Other features which are considered as characteristic for the invention are set forth in the appended claims.
Although the invention is illustrated and described herein as embodied in a fingertip sensor with an integrated key switch, it is nevertheless not intended to be limited to the details shown, since various modifications and structural changes may be made therein without departing from the spirit of the invention and within the scope and range of equivalents of the claims.
The construction and method of operation of the invention, however, together with additional objects and advantages thereof will be best understood from the following description of specific embodiments when read in connection with the accompanying drawings.